Cathodic arc plasma deposition or arc ion plating is the most proliferate technique nowadays for coating on cutting tools, molds, dies and automotive components.
This technology, originated from the development of arc ion evaporator or cathodic arc plasma source in the Soviet Union, has been developed further gradually since it is highly effective technique for industry to deposit thin film for various requirements.
One of the most important development direction of Cathodic arc plasma deposition is to confine plasma, to control the plasma behavior and to reduce the quantity of macroparticles such as molecules or large particles that contaminate in the plasma beam and in the deposited film.
There are many filter apparatuses which had been invented to control plasma and filter the large particles out. These filters use mechanical and/or magnetic field to obtain the required result and they have different pros and cons characteristics.
One of the mechanical apparatus developed in the Soviet Union by A. I. Ryabchikov is a large Venetian-blind filter.
The Ryabchikov's Venetian-blind Filter uses the large frame and places multiple plates inside this fame. The plates are angled in Venetian-blind manner placing between the arc ion evaporator and the substrate of the workpieces. By placing the Venetian-blind filter like this there is no line-of-sight between the arc ion evaporator and workpieces.
When neutral particles or large particles crash into the plates of this Venetian-blind filter, they will implant into the plates or bounce-off to other directions. While plasma which has extremely high energy level can travel through the space between the Venetian-blind filter's plates.
In order to have better plasma transportation out of Venetian-blind filter the specific pattern of electric bias is used to generate the magnetic field around each plate of this filter. And the magnetic field around the filter's plates helps accelerate plasma out of the Venetian-blind structure.
FIG. 1 (Prior Art) shows the principle of Ryabchikov's Venetian-blind filter. The arc ion evaporator 101 generates the plasma beam which consists of Positive ion 109, electron 113 and neutral particles 111. While the positive ion and electron are plasma component, neutral particles can appear in different sizes from atomic size to large particles of several micrometres or larger.
And the Venetian-blind 114 structure used for filtration is built with large rectangular plates placing parallel to one another. If the level of filtration demand is high, these plates will be angled until there is no line-of sight between the arc ion evaporator and the workpieces. When higher plasma transportation is needed, the electric current has to be specifically biased in the direction shown with number 115.
For clearer understanding of principle of Venetian-blind filter, FIG. 2 (Prior Art) shows schematic sketch of this system installed into a vacuum chamber. The arc ion evaporator (101) generates plasma beam beaming in direction towards the Venetian-blind filter (114) structure. The set of filter's plates (or vane or lamella or grill) is angled to block line-of-sight from arc ion evaporator 101 to workpiece substrate 116. And from this FIG. 2 it should be noted that in order to transport plasma out more efficiently, it needs the complex electrical system to bias the Venetian-blind filter. Such complexity limits the usage of this system mainly to the R&D task that requires extra smooth film with very low macroparticle contamination.
FIG. 3 (Prior Art) shows the principle of plasma transportation for Venetian-blind filter. By electrical bias the Venetian-blind filter system as shown in FIG. 1 and FIG. 2, the magnetic field 110 is generated around each plate or lamella 114 of the filter. When plasma beam from arc ion evaporator which consists of plasma 109 and neutral particles 111 runs into the column of filter lamella (or plates), only the plasma will travel through the space between plates, while the neutral particles get stuck and cannot pass through.
FIG. 4 (Prior Art), from U.S. Pat. No. 8,382,963 B2 issued to Frank Weber and Samuel Harris, shows the result of their study on Venetian-blind filter system working in line-of-sight mode. They have found that since the majority of neutral particles do not have trajectory perpendicular to the arc ion evaporator's target surface 102 therefore it is possible to use the depth and space between each plate 114 of filter to reduce some of large particles without the need to angle the plate to block line-of-sight between arc ion evaporator and workpiece surface. Though the coating obtained by this method may not be free from macro particles contamination but it is good enough for coating on cutting tools and automotive components.
Nevertheless, it is the nature of plasma to move in the form of rigid rotor motion (circular movement) but the filters as mentioned above are not positioned along the same line or are inconsistent with the movement of plasma, which are resulting in the unnecessary loss of plasma.
The mathematical formula tan θ crit.=D/S shown in FIG. 4 (Prior Art) is used for finding the critical angle of neutral particles ejected out from arc ion evaporator's target 102 surface to filter's plates 114. If the filter's plate has depth D longer than the critical value or has spacing distance S lower than the critical value obtained from this formula, the neutral particle will be confined inside the filter system.
D is the Filter depth. S is the spacing (distance) between elements (plates). θ is the angle which neutral particle ejects (emission) from the target. θ crit., or the critical angle, is the maximum angle for at least one impact with the filter. 102 is the target material of the arc ion evaporator. 114 is the filter's plate or element. 111 is the neutral particle which crushes into the filter's plate and is confined there. 111a is the neutral particle that can pass through at the critical angle.
It should be noted that the critical angle also depends on the design of Target and arc ion evaporator and by using formula in FIG. 4 (Prior Art). The designer of the system can determine how much large particle filtration is needed.
For better plasma transportation, the said U.S. Pat. No. 8,382,963 B2 still uses the electrical bias according to Ryabchikov's design for magnetic field transportation of plasma.
As the characteristic of said filter is in a form of Venetian-blind filter; thus, it may be possible that some of the plasma may be deviated from or moved outside the set path toward the object. Therefore, in order to push or drive plasma to the right path or direction, it may be necessary to utilize more electrical energy, to the filter and/or the solenoid, to drive such action. Further, Weber's design puts the solenoid around the arc source and that also generates the external magnetic field comparing to the filter body, but the solenoid field tends to diverge plasma out of the center when travelling past the solenoid area. Therefore, to increase the plasma flow and maintain magnetic field line integrity, Weber used the electric bias into the Linear Venetian-blind filter lamella to generate the supporting magnetic field to guide plasma out of the filter system.
Namely, Weber used solenoid placing around the Cathodic arc source working together with the Biased Linear Venetian-blind for their system; thus creating a complex electric bias system that may contribute to very high cost on filter manufacturing. It shows that the magnetic field line of Weber's is external and complex while the magnetic field line of this invention is internal comparing to the filter body and simple.
Both Weber and Ryabchikov used higher current (30-60 A per lamella and 1 kA) to create the magnetic field to transport the plasma while this multiple straight tube filter needs only small current (only 3-5 A is needed) and wherein said plasma further has its own internal kinetic energy to help push or drive itself from the filter system. The filter system according to this invention can, as the result, transport plasma efficiently at lower energy requirement than the existing products or prior arts.
Shown in FIG. 5 (Prior Art) is the Venetian-blind filter system produced by Fraunhofer Research Institute, Dresden, Germany. This is a large system built according to Ryabchikov's design and many arc ion evaporators can be placed on one side of this filter.
However, though the Venetian-blind filter is highly effective in filtration of large particles and has high flexibility to adapt the design according to user demand but some inherent problem renders it less popular in the industrial system. Some examples of these problems are such that the structure is large and requires large room in vacuum chamber of which the effective use of space inside the vacuum chamber is needed for cost reduction. This filter system requires a complex electrical bias to generate the magnetic field, so the cost of building and maintenance of this filter system is also high. Inside the deposition chamber the coating materials will deposit on many parts of vacuum system, so it is needed to have these deposited material removed regularly. The large and complex system means the problem of uninstallation for maintenance, and it also requires larger cleaning or decoating system to remove the deposited material from the filter system.
During the Soviet Union era, I. I. Aksenov et al. studied the angular distribution of neutral particles and large particles from Cathodic arc deposition system and found the majority of neutral particles and large particles tend to emit from arc ion evaporator at 25 to 30 degree of target's surface.
This knowledge reflects in design of many Steered arc ion evaporator from numerous research institutes in the Soviet Union. By placing arc ion evaporator's target deep inside its own port and using solenoid field to drive the plasma out while neutral and large particles crush into the port's surface, the Ion/Neutral ratio becomes higher and therefore the better coatings can be obtained.
FIG. 6 (Prior Art) shows a system which uses this design concept. The arc ion evaporator's target 102 placing deep inside a port 103, or tube in case the target has round face facing into the vacuum chamber, has solenoid 104 generating magnetic field (or solenoid field) to drive the plasma out. The said plasma which is driven out by solenoid field will stream towards the workpiece 116 surface inside the vacuum chamber and deposit coating on the said workpiece surface.
FIG. 7 (Prior Art) shows the magnetic field 110 generated by solenoid coils 104. This solenoid field can guide plasma from arc ion evaporator's target 102 to workpiece's surface 116 since plasma will move along the magnetic field line.
Filter system using solenoid port has some advantages such as space required for such system is low since it can be made quite compact and it can be installed to arc ion evaporator in one to one manner. However, this kind of system is regarded as low filtration efficiency because the port used tends to be large when compared with arc ion evaporator's target diameter, so a significant amount of the neutral particles can reflect out from the wall of solenoid port and land on workpiece surface easily.
And since the price per efficiency ratio is not high, so this filter system is not much proliferate among industry communities outside the former Soviet Union countries.
I the inventor of this present invention had considered about the pros and cons of those said systems above in order to develop a new filter system. The new system has advantage points of the filter system described in the prior art and lessens the disadvantage points.
I the inventor of this present invention use multiple tubes placing parallel to one another instead of using Venetian-blind structure, so that the said multiple tubes can be installed into the port which places in front of the arc ion evaporator. By using such arrangement the volume inside the vacuum chamber can be preserved, since this present invention can be installed in one to one manner to each arc ion evaporator. And when the better plasma transportation is needed, the solenoid system can be used to generate magnetic field for driving more plasma out. By using the solenoid field, the complexity in design and production of the electrical-bias magnetic field generator system for Venetian-blind filter can be avoided.
Moreover, the Venetian-blind system is effective only in some direction, especially when worked in a line-of-sight mode; such as when the plates (or lamella) are placed horizontally without angle, it will leave large space along horizontal line and let more large particles pass out in the left and right direction. If placed vertically without angle, it will leave large space along vertical line and let more large particles pass out in the upper and lower direction.
But since this present invention uses tube structure, therefore it will block large particles from all direction and leave less of them to pass the filter system.
When compared with the pure solenoid port filter used in the Prior Art, this present invention using multiple tubes can effectively block the large particles that reflect out of the wall of solenoid ports. Therefore, this present invention is more effective in filtration and has better efficiency per cost.